1. Field of the Invention.
The present invention relates to circuits for converting a cyclical frequency signal into a current signal proportional to the frequency of the cyclical signal.
2. Description of the Prior Art.
In the prior art there are frequency to current converter circuits that are used in connection with conversion of a "frequency" signal, for example, an output signal from a flowmeter or from a sensor that might sense a parameter, and which delivers a cyclical signal that has a frequency proportional to the value of the parameter. In many instances, switching circuits are utilized wherein each time the frequency signal crosses a threshold in a preselected direction (positive going or negative going), goes positive or exceeds a value, a high voltage signal derived from an independent source is connected to an averaging circuit, and after a set time a low voltage (generally circuit common) is switched to the averaging circuit and the average voltage value is used to control flow.
One major problem inherent in this type of conversion is getting a nonzero output current (for example 4 milliamps) for a zero value input signal (i.e. zero frequency). Usually some type of special zeroing circuit is needed in the output circuit to null against the positive output feedback signal that is present when the 4 milliamps current is flowing in the output current path.
The sources also are not well regulated in prior devices, and thus any control signal derived from the sources is not regulated to be precise and provide a precise output.